Why translate the names?
And it is done for kings, queens, popes and maybe some others:
Normally, you won't translate names, but these are the Dutch equivalents, it's good to know what name it is in English when you hear a name :) [I guess they accept the original names too]
It is also gives you a chance to work on the letters pronunciation, as you need to transfer the sound of William into Dutch sounds.
Why not: Zijn jullie namen willem en roos? Or am i englishifying it?
That's "Are your names William and Rose?" In english you might say, "Your names are William and Rose?" kind of as a clarification question. That's what this is
Just working from the examples of schaap -> schapen, and naam -> namen, is it a rule that singular nouns with an aa in the middle have only one a in the plural? Bedankt!